The present invention relates, in general, to a load sharing mechanism for power transmissions and in particular to a load sharing mechanism for a compound planetary gear transmission with a set of stepped planet gears.
Rotary wing aircraft typically use a high-speed turbine engine to drive the rotor or propeller. A main gear transmission between the engine and the rotor is necessary to transmit engine power while reducing the engine speed to achieve the appropriate rotor speed. The main gear transmission is usually the heaviest subsystem in the drive train of the aircraft. Increasing power throughput and reducing the weight of the transmission is very desirable for modern rotary wing aircraft.
One effective way to improve power density in a main gear transmission is to divide the input torque supplied from the engine or other power source across multiple paths through the transmission to the output shaft. Each discrete path requires a smaller individual gear member, which leads to an overall transmission design that is lighter in weight, is compact in size, and has smaller gear face widths due to the reduced loads applied at each gear mesh. The smaller, but numerous, gears also require smaller supporting bearings, which correspondingly have an increased operational life span due to the reduced application of torque. An exemplary power dense planetary gear transmission consists of a compound planetary gear-train having a set of stepped planet gears. Each stepped planet gear includes a large planet gear driven by a sun gear coupled to the input shaft and a small drive planet pinion. The stepped planet gears may have a flexible shaft between the large planet gear and the small drive planet pinion. The small drive planet pinions are each disposed between, and engaged with, the outer circumference of a first reaction or idler sun gear and the inner circumference of a second reaction or ring gear, and are secured to the respective large gears by a shaft fitted through a cluster gear support bearing. A planet carrier supports a set of small and simple idler planet pinions to share the torque, distributing load carried by the main gear transmission among the drive planet pinions and the idler planet pinions disposed between the ring gear and the idler sun gear. The idler planet pinions have non-floating shafts with respect to the planet carrier.
A second exemplary transmission is a split-torque face gear transmission, where a stepped gear is used to drive a primary face gear and an idler face gear; the stepped gear being sandwiched between the primary face gear and the idler face gear. The stepped gears have a floating or pivoting shaft, with small idler gears mounted to fixed shafts being used as crossover gears to provide multiple power paths to share the load from the input shaft to the output shaft.
When splitting the driving torque loads applied through a transmission from an input shaft to an output shaft between two reaction gears or pathways, either through a compound planetary gear-train transmission or a split-torque face gear transmission, it is preferable to provide for an optimized load distribution among the various drive plant pinions and idler planet pinions between the reaction gears and primary gear in order to achieve a maximum load carrying capacity for the transmission. Accordingly, it would be advantageous to provide a method by which supporting components within the transmission can be selectively positioned in order to achieve an optimized load distribution.